Hydraulic fluid



Patented Apr. 28, 1953 HYDRAULIC FLUID 'Forrest J. Watson, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Califl, a corporation of Delaware No Drawing. Application June 9, 1950, Serial No. 167,261

16 Claims. 1

The present invention relates to an improved oleaginous composition especially useful at low Operating temperatures. More particularly, it is directed to a composition containing a major amount of a special mixture of organic phosphates. I

Compositions suitable for special purposes, such as low-temperature lubrication and the operation of hydraulic mechanisms, require a combination of properties which ordinary oil fails to meet in many respects. The special fluids contemplated in this invention are useful in hydraulic systems, particularly aircraft hydraulic systems, recoil mechanisms, fluid-drive power transmissions, as well as in special lubricating applications which require the combinations of properties described below. The properties which are required for safe and satisfactory low-temperature operation include low pour point so that the composition will operate at temperatures at least as low as 40 F. to 60 F. Another important property which is desirable for such uses is a flat viscosity-temperature curve, i. e., a high viscosity index, so that the oil is operable over a wide range of temperatures, such as are encountered in the operation of aircraft and in certain other industrial applications. portant property which must be considered for both commercial aircraft and military use is minimum flammability. Other inherent qualities include a relatively high boiling point, low corrosion characteristics and low oxidation susceptibility. Y

Numerous compositions have been suggested for the above purposes, none of which possess the unique combination of desirable characteristics inherent in the compositions of the present invention. The lower trialkyl phosphates exhibit high wear characteristics, are somewhat flammable, due in part to their volatility, and at low temperatures exhibit incompatibility with thick-' 2 tuted triaryl phosphates, such as triphenyl phosphate, cannot be used, due to the fact that they are solids even above room temperature. The mixed phosphates, that is the phosphates which contain both alkyl and aryl groups, such as diphenyl octyl phosphate, exhibit extremely high copper and cadmium corrosion and are partially incompatible with polymerized methacrylic acid esters at low temperature.

It is an object of the present invention to provide oleaginous compositions useful for the operation of apparatus, such as hydraulic systems, at low temperatures and 'with a maximum of safety from fire. It is another object of the present invention to provide compositions especially useful as industrial and aircraft hydraulic fluids. It is still another object of the present invention to provide improved organic phosphate compositions for the uses described hereinbefore.

Now in accordance with the present invention, it has been found that the above and other objects may be obtained by a special mixture comprising a trialkyl phosphate and a triaryl phosphate. More specifically, in accordance with the invention it has been found that a mixture comprising a trialkyl phosphate wherein each of the alkyl groups has not over 12 carbon atoms, preferably from four to nine carbon atoms, and a triaryl phosphate containing one or two phenyl groups is an especially effective, substantially non-flammable lubricant and hydraulic fluid. The above mixtures may further be improved by the addition of viscosity index improvers, such as the polymerized esters of methacrylic acid, alkylated styrene polymer, polyisobutylene, polymerized organic silicones, polymerized styrene and vinyl compounds, etc., and by the addition of certain corrosion inhibitors and anti-oxidants, as more particularly described hereinbelow. The individual components of the compositions of the subject invention are fully described and discussed below.

THE TRIALKYL PHOSPHATES The trialkyl phosphates to be used in the present invention may be present in amounts from 50% to 90% by weight and preferably from to by weight. The trialkyl phosphates which give optimum results are those wherein each of the alkyl groups has not over 12 carbon 3 atoms, 1. e., below 13 carbon atoms, preferably from four to nine carbon atoms. The alkyl groups may be either in a straight-chain or in a branched chain configuration, the latter being preferred. A single trialkyl phosphate may contain the same alkyl group in all three positions or may possess a mixture of different alkyl groups. Mixtures of various trialkyl phosphates may be used. Suitable species of trialkyl phosphates which may be employed in the compositions of the invention include tributyl phosphates, trihexyl phosphates, trioctyl phosphates, especially the branched homologues, such as tri(2-ethylbutyl) phosphate and tri(2-ethylhexyl) phosphate, also trinonyl phosphates, such as tris(3,5,5- trimethylhexyl) phosphate and the other tri alkyl phosphates and their branched homologues. The physical characteristics of typical phosphates are given below:

THE VISCOSITY INDEX IMPROVING AGENTS Viscosity index improving agents which may be added in varying amounts to compositions of the. subject invention to meet various industrial requirements include alkylated styrene polymer, polyisobutylene, polymerized organic silicones, polymerized styrene and vinyl compounds, etc.

Properties of various trialkyl phosphates ri-2- I Tri-n- Tri-n- 1 T Tri-n- Tri-n- Ethylthyltrimcthylbutyl amyl i butyl hcxyl hexyl octyl hexyl) Boiling Point, 0., 1 mm 113. 8 129. 1 146. 4 166. 1 Pour Point, -F Freezing Point, F-.- -50 -50 -50 50 Open-Cup Flash, F 340 355 410 Open-Cup'Fire, F L 380 380 445 Viscosity, Centistokesat 210 1.06 1.36 1.68 1.76 Viscosity, Centistokcs atl00 F 2. 66 3. 79 4 79 4. 75 Viscosity, Oentistokes at -40 F; 4 4701 46.0 114 240' 153 Viscosity Index V 91 122 150 1 Lower than.

THE TRIARYL PHOSPHATES where X is the phenyl radical, Y is a substituted phenyl radical and Z is selected from the group consistingof. phenyl andsubstituted phenyl radicals. The substituted. phenyl radical is preferably an aliphatic substituted phenyl radical, especially a. lower aliphatic. substituted phenyl radical containing not more than 5 carbon atoms in a substituent group, such as a cumenyl radical. The alkyl substituted phenyl radicals, such as the methyl substituted phenyl radicals, e. g., tolyl, xylyl and pseudocumyl radicals, are especially useful in the compositions of the invention.

Typical v isobutene, and alkylated styrene polymers which may beused as viscosity indeximprovers.

have the following physical properties:

- Alkylatcdstyi q' renc polymerbutene Sold Sold I commercially. mercian under. the. underthg trade'name' trade-name P'ammne Santodex Gravity, A. 1?. IL. 29 25.9 S. U. V. at 1O0 F 42,600. 30, 000 S. U. VJ at 210 F; 3,000 1,900

1 Saybolt Universal viscosity.

In general the. aboyeviscosity index. improving.

agents have an average molecular weight. of from about 5,000 to about 35,000.

The preferred agents to be usedin thesubject compositions include polymerized esters of the acrylic acidseries, such as acrylicacid esters. and

more particularly,.me.thacrylic acid esters. The.

latter are readily. available. as commercial products and are. sold. under. the. trade. name. Acryloid. The polymerized? estersto. be used. should.

have molecular. weights. from about. 5,000 to. about 25,000, preferably 5,000 to. about 15,000. It is understood that this. is an average. figure for the mixtures of. polymers which. is, usually present due to the greater or lesser. degree of polymerization.

The acids should be esterified with. aliphatic alcohol'shavingtwo to fifteen carbon atoms and the polymers may be homopolymers of a single. ester or maybecopolymersof a mixture of such.

aesaeer:

has a viscosity of 55 centistokes (cs.) at 210 F.

in a standard base stockhaving a viscosity of 3.3 cs. at 100 F. Acryloid HF8125 is a solution of the polymerized ester in a petroleum base stock of a 300 F. flash point mineral oil and a 30% by weight solution has a viscosity of 125 cs. at 210 F. in a standard base stock having a viscosity of 3.3 at 100 F.

.The above viscosity index improving agents may be present in effective minor amounts up to about 20-25% by weight of the total composition. In general, it is desirable to employ these agents in an amount between about 2% to about 10% by weight, preferably between 5% and by weight of the total composition.

For certain special compositions such as industrial hydraulic fluids the viscosity index improving agents may be present in an amount between about 10% and by weight of the total composition.

THE OXIDATION AND CORROSION INHIBITORS While the compositions described above exhibit excellent and satisfactory corrosion and stability characteristics, it is preferable to include certain corrosion inhibitors and anti-oxidants to protect the equipment for extended use. It has been found that the combination of an epoxide compound and a sulfur-containing organic compound is especially effective as a corrosion inhibitor and an anti-oxidant for the compositions of the subject invention.

The epoxide compounds alone are effective corrosion inhibitors for the compositions of the invention, and may be present in an amount between about 0.5% and 5% by weight of the total composition. Of the epoxide compounds the glycidyl ethers are most highly preferred and of these, glycidyl ethers containing one carbocyclic group directly attached to the ether oxygen atom, suchas the glycidyl aryl ethers, provide maximum protection against corrosion, especially of copper and cadmium. Specific glycidyl ethers which may be employed include glycidyl phenyl ether, g lycidyl benzyl ether, glycidyl cyclohexyl ether and glycidyl o-cresyl ether. Other epoxide compounds which may be employed include the lower glycidyl alkyl ethers, such as glycidyl methyl ether and gylcidyl isopropyl ether as well as isobutylene oxide, butadiene monoxide, styrene oxide, cyclohexylene oxide, cyclopentene oxide, decene oxide, 2,3-epoxybutane, 1,2-epoxybutane, ethylene oxide, epi- V chlorohydrin, etc.

While the above epoxide organic compounds alone are against corrosion and oxidation is afforded by the combination of the above epoxide compounds with a sulfur-containing organic compound. Suitable sulfur-containing organic compounds for the above combination are the hydrocarbyl sulfides, especially the hydrocarbyl disulfides,

satisfactory, excellent protection such as the dialkyl disulfides and diaryl disulfides and may be present in an amount between about 0.05% and 1% by weight of the total compositions. Benzyl disulfide, butyl disulfide and wax disulfide are particularly useful.

The wax disulfide preferred in the compositions of the invention is a reaction product of sodium disulfide and a chlorinated paraffin wax and may be prepared in the following manner.

Approximately 5.5 parts by weight sodium disulfide is dissolved in about 2.2 parts by weight of water, the solution is heated and about .7 part by weight sulfur dissolved therein with stirring.

The resulting solution together with about 5.2 parts by weight of a chlorinated paraffin wax (chlorine content approximately 30% by weight) and about 10 parts by weight each of denatured alcohol and naphtha were charged into an autoclave and stirred therein at a temperature of about 145-150" C. for 10 hours. The-maximum pressure developed was about 220-230 p. s. 1..

After cooling about 16 parts by weight water was added and thoroughly admixed. Two layers separated upon standing, a naphtha layer and an aqueous layer. The naphtha layer was separated, dried over anhydrous sodium sulfate, filtered and the naphtha distilled off therefrom under reduced pressure the maximum kettle temperature being not greater than C. There was obtained 21.6-parts-by weight of product (wax disulfide) as a viscous,oil-soluble, darkcolored liquid. A typical analysis of a wax disulfide employed in the compositions of the invention is set forth below:

Specific gravity 20/4 1.024 Molecular weight 1050 Sulfur- 20-23% wt. Chlorine 1.5-4% wt.

and halogenation of olefins such as ethylene,

propylene, etc.

Other suitable sulfur-containing compounds are di-iso-amyl disulfide, di-n-propyl disulfide, dibenzyl disulfide, diphenyl disulfide, alkyl mercaptans having at least 7 carbon atoms, in general compounds exemplified by the general formula R-S-S-R where R and R denote alkyl or aryl groups.

Compositions of the invention which are especially useful and effective include between about 0.5% to 3% by weight of an epoxide compound such as glycidyl phenyl ether and betweenabout 0.05% and about 0.5% by weight, preferably between 0.05% and 0.2% by weight of an organic sulfide such as wax disulfide.

While the above types of corrosion inhibitors are preferred for use in the present invention, other inhibitors may be used as well, such as hydroxy aromatic carboxylic acids, alkyl malonic acids, the polyvalent metal salts of hydrocarbon sulfonic acids,.amines, amino phenols, and other substituted phenols.

In general, if corrosion inhibitors are employed in the present compositions they may be present in amounts from about 0.5% to about 5.0% by weight, preferably from about 1% to about 2% by weight.

OTHER COMPONENTS The compositions of the invention may be modified by the addition of other suitable ingredients as long as they are in minor proportions, relative to the mixture of phosphates described. Such. optional ingredients include mineral oils, synthetic oils, and flame-proofing compounds.

Suitable synthetic lubricants which may be employed include especially the polymerized alkylene oxides or glycols, such as polymeric 1,2- propylene oxides and polymerized trimethylene glycol. Another type which has been found satisfactory includes esters of dicarboxylic acids, such as the sebacates and adipates, as well as other acids having four to twelve carbon atoms, said acids being esterified with alcohols having two to fifteen. carbon atoms, such as di.(2-ethylhexyl)' sebacate.

Flame-proofing agents which may be added are exemplified by methylene iodide or chlorinated hydrocarbons and may be present up to about 10% by weight of the total composition.

The following examples illustrate the present invention.

Example I The following composition was prepared by stirring the following ingredients together:

pump operated at 1000 lbs. p. s. i. for 50 hours at a temperature of 160 F. The hydraulic fluid completed approximately 15,000 cycles through the pump under these conditions. This type of 5 pump is similar to that employed on Army and Navy aircraft. It was found. that the acid neutralization number of the used oil was substantially the same as that of the original oil and that the viscosity at 100 F. dropped about twothirds as much as. a comparable. petroleum base.

hydraulic fluid. similar test was also carried outat 3000 lbs. 13.5. i. for a period of 350 hours and a. fully satisfactory performance was obtained.

Example IV obtained. For purposes of comparison, the test data of a composition hereafter called Example Ia, similar to the composition described in Example I but replacing the diphenyl. cresyl. phos- Ingredient: Parts by weight phate with an equal amount of tricresyl phos- Y YD p sphate 83.5 phate, i. e., a triaryl phosphate wherein all the Diphenyl cresyl phosphate 10 aryl groups are tolyl radicals, are also included. Acryloid HF 855 .5 The results obtained are setforth in Table A Glycidyl phenyl ether 1 below:

TABLE A CorrosionWeight loss mgu/cm. Oxidation Composition Tested Acid. Percent 1 Cu Mg Fe ca Al Neut. $5553". No. 0 y at 100 1.

Example 4.04 0.107' 0 2.01 0.01 11.7 20 ExampleI 1.86 1. 12 +0.07 1. 65 +007 23.0 41 Example 11 0. 23 0.01 0.01 0. 02 0 0. 2e 4 The above composition had the following properties:

Viscosity, centistokes F 1700 Viscosity, centistokes +100 F 14.5 Viscosity, centistokes +2l0 F 3.96 Viscosity index. (ASTM) 192 Acid Neut. No 0.42

Example H The following composition was prepared by stirring the following ingredients together:

Ingredient: Parts by weight Tris(2-ethylhexyl) phosphate 83.5- Diphenyl cresyl phosphate 10 Acryloid HE 855 5.5- Glycidyl phenyl ether .9 Wax disulfide .1

The above composition had the following properties:

Viscosity, centistokes -40 F 1750 Emample III The composition described in Example II was used as the hydraulic fluid in aVickers hydraulic The above tests, as indicated by the data obtained, eifectively demonstrate the outstanding superiority of compositions according to themvention (see Example II) wherein an epoxide and a sulfur-containing compound are present over all the other compositions tested. The tests also demonstrate that compositions according to the invention are considerablyless corrosive tomost metals than similar compositions containing a triaryl phosphate, such as tricresyl phosphate, which triaryl phosphateis not of thetype inaccordance with and described in this invention.

Example V For certain uses, such as in aircraft hydraulic systems, it is desirable. to employ a hydraulic. fluid which has a relatively lowviscosity at a reduced temperature. A typical requirement,AMS-3150A of the SAllis that the hydraulic fluid at a temperature of -4=0 F. shouldhave a viscosity not greater than 2000 centistokes for. a so-called 2,000 grade hydraulic fluid. It. has been found that hydraulic fluids. according to. the inventionwhich contain diphenyl cresyl phosphate. are most suitable and preferable in compositions which meet the aforesaid requirement.

Illustrative of the above, various compositions. all of which have approximately equal viscosity- (l-centistokes) at 210 F., were prepared, using a trioctyl phosphate-polymerized ester of methacrylic: acid blend as the; base. At av temperature Corrosion was negligible. A

of. --40. F: thebase' blend had aviscosity ofl350 centistokes (cs.). Table B set forth below, illustrates the superiority of diphenyl cresyl phosphate as an ingredient in hydraulic fluid compositions with respect to low temperature viscosity.

TABLE B Viscosity at 40 F.

Ingredient %lwt. of %lwt. of comp. comp.

Tricresyl phosphate l, 600 1, 950 Diphenyl cresyl phosphate 1, 510 1, 700

The above-indicated data demonstrate that hydraulic fluids containing a trialkyl phosphate and a triaryl phosphate according to the invention, specifically diphenyl cresyl phosphate, as the main ingredients give a greater margin of safety in meeting low temperature viscosity requirements than a similar composition containing a triaryl phosphate, specifically a tricresyl phosphate, not in accordance with the invention.

Example VI The following composition was prepared by stirring the following ingredients together:

Ingredient: Parts by weight Tris(2-ethylhexyl) phosphate 64 Acryloid HF8125 Diphenyl cresyl phosphate 10 Glycidyl phenyl ether .9 Wax disulfide .1

The above composition was a clear, somewhat viscous liquid and had the following viscosity:

Viscosity, centistokes +100 F 67.2

I claim as myinvention:

1. A composition of matter comprising 5090 per cent by weight of a trialkyl phosphate, each alkyl radical of which contains 4 to 9 carbon atoms; 5-25% by weight of a triaryl phosphate having the general formula:

where X is the phenyl radical, Y is an alkyl substituted phenyl radical wherein each alkyl group therein contains not more than five carbon atoms and Z is selected from the group consisting of phenyl and alkyl substituted phenyl radicals wherein each alkyl group. therein contains not more than five carbon atoms; 2-20 by weight of a linear polymer of methacrylic acid esters having a molecular weight within the range 5000 to 25000; 0.5 to 3.0% by weight of an expoxide'compound selected from the group consisting of.

where X is the phenyl radical, Y is an alkyl substituted phenyl radical wherein each alkyl group therein contains not more than 5 carbon atoms and Z is selected from the group consisting of a phenyl radical and an alkyl substituted phenyl radical, wherein each alkyl group therein contains not more than 5 carbon atoms; 2-20% by weight of a linear polymer of methacrylic acid esters having a molecular weight within the range of 5000 to 25000; 0.5 to 3.0% by weight of an epoxide compound selected from the group consisting of glycidyl hydrocarbyl ethers and hydrocarbon epoxides and 0.05 to 0.5% by weight of a hydrocarbyl sulfide.

3. A composition of matter comprising -90% by weight of a trialkyl phosphate, each alkyl radical of which contains 4 to 9 carbon atoms; 5-25% by weight of a triaryl phosphate having the general formula:

where X is the phenyl radical, Y is an alkyl substituted phenyl radical wherein each alkyl group therein contains not more than 5 carbon atoms and Z is selected from the group consisting of a phenyl radical and an alkyl substituted phenyl radical, wherein each alkyl group therein contains not more than 5 carbon atoms; 2-20% by weight of a linear polymer of methacrylic acid esters having a molecular weight within the range 5000 to 25000; 0.5 to 3.0% by weight glycidyl phenyl ether and 0.05 to 0.5% by Weight of a wax disulfide.

4.. A composition of matter comprising 50-90% by weight of a trialkyl phosphate, each alkyl radical of which contains 4 to 9 carbon atoms; 5-25% by weight of diphenyl cresyl phosphate; 2-20% by weight of a linear polymer of methacrylic acid esters havin a molecular weight within the range of 5000 to 25000; 0.5 to 3.0% by weight of an epoxide compound selected from the group consisting of glycidyl hydrocarbyl ethers and hydrocarbon epoxides and 0.05 to 0.5% by weight of a hydrocarbyl sulfide. I

5. A composition of matter according to claim 4 wherein the epoxide compound is glycidyl phenyl ether and the sulfur-containing organic compound is a wax disulfide.

6. A composition of matter comprising 50-90% by weight of a trioctyl phosphate; 5-25% by weight of diphenyl cresyl phosphate; 220% by weight of a linear polymer of methacrylic acid esters having a molecular weight within the range 5000 to 25,000; 0.5 to 3.0% by weight of glycidyl phenyl ether and 0.05 to 0.5% by weight of a wax 7. A composition possessing lubricating properties which comprises: 5090% by weight of a trialkyl phosphate, each alkyl radical of which contains less than 13 carbon atoms; 5-25% by weight of a triaryl phosphate having the general formula: 1

where X is the phenyl radical, Y is an alkyl substituted phenyl radical wherein each alkyl group therein contains not more than five carbon atoms and Z is selected from the group consisting of phenyl and alkyl substituted phenyl radicals wherein each alkyl group therein contains not more than five carbon atoms, and an effective minor amount of a viscosity index improving agent selected from the group consisting of polymerized, unsaturated hydrocarbons, polymerized organic ,sil-icones, polymerized esters of acrylic .acid, and polymerized estersof methacrylic acid, said viscosity index improving agent having a molecular weight from-about 5000-to about 25,000.

-8. A-composition of matter comprising 50-9.0% by weight of .a trinonyl phosphate; -25% by weight -.of diphenyl cresyl phosphate and an effective iminor amount of a viscosity index improving agent selected :from the group consisting of polymerized, unsaturated hydrocarbons, polymerized organic silicones, polymerized esters .of acrylic acid, and polymerized esters of .methacrylic acid, said viscosity index improving agent .having a molecular weight from about 5,000 to about 25,000.

9. A composition of matter according to claim 8 wherein the trinonyl phosphate is tris(3,5,5- trimethylhexyl) phosphate.

10. A composition of matter consisting of the following ingredients:

Ingredient: .Parts by weight Tris(2-ethylhexyl) phosphate .64 .Diphenyl .cresyl phosphate 10 Methacrylic .acid ester polymer having .a molecular weight of fromabout 5000 .to about 25,000 12.5 Mineral oil carrier for said polymer 12.5 Glycidyl phenyl ether .9 Wax disulfide .1

11. A composition of matter consisting essentially of the following ingredients in approximately the following proportions:

12. A composition of matter consisting of the following ingredients:

Ingredient: Parts by weight Tris(2-ethylhexyl) phosphate 33.5 Diphenyl cresyl phosphate 1-0 .Methacrylic acid ester polymer having a molecular weight of from about 5,000 to about 25,000 2.75 Mineral oil carrier for said polymer 2.75 Glycidyl phenyl ether 9 Wax disulfide ..1

13. A composition possessing lubricating properties-which comprises -90% -by weight of a .trialkyl phosphate, each alkyl radical of which contains less than 13 carbon atoms; 5-25% by weight of a triaryl phosphate, having the general formula where .X is the phenyl radical, Y is .an-alkylsubstituted phenyl radical wherein each alkyl group therein contains not more than 5 carbon atoms and .Z is selectedfrom the group consisting of phenyl and alkyl-substituted phenyl radicals wherein each alkyl group therein contains not more than 5 carbon atoms, and an effective minor amount sufficient to raise the viscosity index of said composition of a polymerized ester of methacrylic acid having a molecular weight from about 5000 to about 25,000.

14. A composition of matter comprising '50-90% by weight of a trialkyl phosphate, each 'alkyl radical of which contains 4 to 9 carbon atoms; 5-25% by weight of triaryl phosphate having the general formula o=P-o-Y 0-2 wherein 'X is "the "phenyl radical, Y and 'Z are alkyl-substituted phenyl radicals wherein each a-lkyl constituent therein contains not more than 5 carbon atoms and an effective minor amount sufficient to raise the viscosity index of said composition of a polymerized ester of methacrylic acid having a molecular weight from about 5000 to about 25,000.

15. A composition possessing lubricating properties which comprises 50-90% by weight of trialkyl phosphate, each alkyl radical of which contains from 4 .to 9 carbon atoms; 5-25'% .by weight .of a triaryl phosphate having fthegeneralformula o-X O=PO.Y

0-2 wherein X and Y are phenyl radicals and Z is an alkyl-substituted phenyl radical wherein each alkyl group therein contains not more than 5 carbon atoms and. an eflective minor amount suiiicient to raise the viscosity index-of said composition of a polymerized ester .of methacrylic acid having an average molecular weight between 5000 and 25000.

16. A composition possessing lubricating properties which comprises .50-% by weight of trioctyl phosphate, 5-25% by weight of diphenyl cresyl phosphate and an efiiective minor amount of a viscosity index improving agent comprising a polymerized ester of .methacrylic acid having an average molecular weight between about 5000 and 25,000.

FORREST J. WATSON.

References Cited in the file of this patent UNITED STATES PATENTS Number 

1. A COMPOSITION OF MATTER COMPRISING 50-90 PER CENT BY WEIGHT OF A TRIALKYL PHOSPHATE, EACH ALKYL RADICAL OF WHICH CONTAINS 4 TO 9 CARBON ATOMS; 5-25% BY WEIGHT OF A TRIARYL PHOSPHATE HAVING THE GENERAL FORMULA: 